Method of enhancing conductivity from post frac channel formation

Abstract

A method of enhancing conductivity within a hydrocarbon-bearing reservoir by building proppant pillars in a spatial arrangement in fractures created or enlarged in the reservoir. Two fluids of differing viscosity and stability are simultaneously pumped into the reservoir. The fluids contain identical proppants which include a proppant which is neutrally buoyant in the fluid and a proppant which is not neutrally buoyant in the fluid. Vertically extending pillars are created within the formation when the fluids are destabilized and the heavier proppant is then released from the destabilized fluids. The area between the pillars may be held open by the presence of the neutrally buoyant proppant in the remaining fluid. Fluid produced from the hydrocarbon-bearing reservoir is then flowed at least partially through channels between the vertically extending pillars.

What is claimed is: 
     
       1. A method of enhancing the productivity of hydrocarbons from a hydrocarbon-bearing formation which comprises:
 (A) subsequent to creating or enlarging one or more fractures within the subterranean formation, simultaneously pumping into a well penetrating the hydrocarbon-bearing formation at least two proppant-laden slurries of different viscosity and stability wherein one of the slurries is more viscous and more stable than another of the slurries which is less viscous and less stable, wherein the viscosity ratio of the more viscous slurry to the less viscous slurry is a minimum of 1.3:1 and further wherein the proppant in each of the proppant-laden slurries is the same, the proppant comprising a relatively lightweight proppant and a heavier proppant having an apparent specific gravity greater than or equal to 2.65; 
 (B) degrading the less viscous slurry and releasing the heavier proppant from the less viscous slurry; 
 (C) consolidating the released heavier proppant from the less viscous slurry on an upper portion of the more viscous slurry and/or at a pinch point in the width of the fracture; 
 (D) introducing the released heavier proppant from the less viscous slurry into the width of the fracture and creating two or more pillars within the fracture from the released heavier proppant; 
 (E) degrading the more viscous slurry and releasing the heavier proppant from the more viscous slurry onto the created two or more pillars; and 
 (F) creating a channel in the subterranean formation between the two or more pillars with the relatively lightweight proppant in the less viscous slurry and the more viscous slurry. 
 
     
     
       2. The method of  claim 1 , further comprising creating a partial monolayer between the two or more pillars with the relatively lightweight proppant. 
     
     
       3. The method of  claim 1 , further comprising maintaining fracture conductivity between the at least two pillars by bracing the area between the at least two pillars with the relatively lightweight proppant. 
     
     
       4. The method of  claim 1 , further comprising repeating altering the stability of the less viscous and less stable slurry and repeating step (A), wherein the stability of the less viscous and less stable slurry is changed by varying the breaker, crosslinking agent, gel stabilizer, viscosifying agent or pH buffer or a combination thereof. 
     
     
       5. The method of  claim 4 , wherein at least one of the following conditions prevail:
 (a) each of the at least two proppant-laden slurries contains the same breaker; 
 (b) each of the at least two proppant-laden slurries contains the same crosslinking agent; 
 (c) each of the at least two proppant-laden slurries contains the same gel stabilizer; 
 (d) each of the at least two proppant-laden slurries contains the same viscosifying agent; or 
 (e) the pH of the at least two proppant-laden slurries is the same. 
 
     
     
       6. The method of  claim 1 , further comprising repeating altering the stability of the less viscous and less stable slurry and repeating step (A), wherein the stability of the less viscous and less stable slurry is changed by varying the quantity of breaker, crosslinking agent, gel stabilizer, viscosifying agent or pH buffer or a combination thereof. 
     
     
       7. The method of  claim 6 , wherein at least one of the following conditions prevail:
 (a) each of the at least two proppant-laden slurries contains the same breaker; 
 (b) each of the at least two proppant-laden slurries contains the same crosslinking agent; 
 (c) each of the at least two proppant-laden slurries contains the same gel stabilizer; 
 (d) each of the at least two proppant-laden slurries contains the same viscosifying agent; or 
 (e) the pH of the at least two proppant-laden slurries is the same. 
 
     
     
       8. The method of  claim 1 , wherein the amount of proppant in the two proppant-laden slurries is the same. 
     
     
       9. A method of pillar fracturing a hydrocarbon-bearing subterranean formation penetrated by a well, the method comprising:
 (A) after the creation or enlargement of fractures within the subterranean formation, simultaneously pumping into a well penetrating the hydrocarbon-bearing reservoir at least two proppant-laden fluids of differing viscosity, wherein the proppant of each of the at least two proppant-laden fluids is the same, the proppant comprising a proppant neutrally buoyant in the fluid and a heavier proppant having an apparent specific gravity greater than or equal to 2.45, wherein the amount of neutrally buoyant proppant and heavier proppant in each of the at least two proppant-laden carrier fluids is the same; 
 (B) viscous fingering the two proppant-laden fluids of differing viscosity within the created or enlarged fracture and developing a placement pattern for the heavier proppants of the less viscous fluid and the more viscous fluid in the fracture; 
 (C) shutting in the well; 
 (D) releasing the heavier proppant from the less viscous fluid; 
 (E) consolidating the released heavier proppant from the less viscous fluid on an upper portion of the more stable fluid and/or at a pinch point in the width of the fracture; 
 (F) creating at least two vertically extending pillars within the formation from the heavier proppant released from the less viscous fluid wherein the placement of the at least two vertically extending pillars is determined by the viscous fingering pattern of the two proppant-laden fluids of step (B); 
 (G) degrading the more viscous fluid and building at least two vertically extending pillars from the heavier proppant released from the more viscous fluid; 
 (H) creating conductive channels within the subterranean formation between the at least two vertically extending pillars; and 
 (I) bracing open the fracture between the at least two vertically extending pillars with the neutrally buoyant proppant from the more stable and/or less stable fluid. 
 
     
     
       10. The method of  claim 9 , further comprising creating a partial monolayer between the at least two vertically extending pillars with the neutrally buoyant proppant. 
     
     
       11. The method of  claim 9 , further comprising repeating step (A) at a pulse rate between from about 15 seconds to about 5 minutes. 
     
     
       12. The method of  claim 9 , wherein the difference in viscosity between the more viscous fluid and the less viscous fluid is between from 200 to 1500 cP. 
     
     
       13. The method of  claim 9 , wherein at least one of the following conditions prevail:
 (a) the more viscous fluid and the less viscous fluid contain the same breaker and further wherein the amount of breaker in the less viscous fluid is more than the amount of breaker in the more viscous fluid; or 
 (b) the more viscous fluid and the less viscous fluid contain the same gel stabilizer and further wherein the amount of gel stabilizer in the less viscous fluid is less than the amount of gel stabilizer in the more viscous fluid. 
 
     
     
       14. The method of  9 , wherein at least one of the following conditions prevail:
 (a) the less viscous fluid is less stable than the more viscous fluid by the amount of pH buffer present in the less viscous fluid; or 
 (b) the more viscous fluid and the less viscous fluid contain the same viscosifying agent and wherein the amount of viscosifying agent in the less viscous fluid is less than the amount of viscosifying agent in the more viscous fluid. 
 
     
     
       15. A method of pillar fracturing a hydrocarbon-bearing subterranean formation penetrated by a well, the method comprising:
 (A) subsequent to the creation or enlargement of fractures within the subterranean formation, pumping at least two slurries of differing viscosity simultaneously into the wells, wherein each of the slurries contains suspended proppant and wherein the proppant in the at least two slurries is the same and is a mixture of proppant neutrally buoyant in the fluid of the slurry and a heavier proppant having an apparent specific gravity greater than or equal to 2.45 and further wherein the amount of neutrally buoyant proppant and heavier proppant in each of the at least two proppant-laden slurries is the same; 
 (B) controlling the shape and/or placement of a proppant pillar to be created within the subterranean formation during the simultaneous pumping of the proppant-laden slurries while the proppant-laden slurries are in a dynamic state by fingering the proppant-laden slurries into the created or enlarged fractures; 
 (C) releasing the heavy proppant from the less viscous slurry while the less viscous slurry is in a static state; 
 (D) creating at least two vertically extended pillars within the subterranean formation from the heavy proppant released from the less viscous slurry; 
 (E) releasing the heavy proppant suspended in the more viscous slurry while the more viscous slurry is in a static state; 
 (F) building onto the at least two vertically extended pillars from the proppant released from the more viscous slurry; 
 (G) creating conductive channels within the subterranean formation between the vertically extending pillars; and 
 (H) bracing open the fracture between the vertically extended pillars with the neutrally buoyant proppant from the more viscous and/or less viscous slurry. 
 
     
     
       16. The method of  claim 15 , further comprising creating a partial monolayer of proppant from the neutrally buoyant proppant in the area between the vertically extended pillars. 
     
     
       17. The method of  claim 15 , wherein the less viscous fluid is less stable than the more viscous fluid due to the presence of and/or amount of breaker, crosslinking agent, gel stabilizer, pH buffer or viscosifying agent in the less viscous fluid. 
     
     
       18. The method of  claim 15 , wherein the viscosity ratio of the more viscous slurry to the less viscous slurry is a minimum of 1.3:1. 
     
     
       19. The method of  claim 15 , wherein the difference in viscosity between the more viscous slurry and the less viscous slurry is between from 200 to 1500 cP. 
     
     
       20. The method of  claim 15 , wherein at least one of the following conditions prevail:
 (a) the more viscous fluid and the less viscous fluid contain the same breaker and further wherein the amount of breaker in the less viscous fluid is more than the amount of breaker in the more viscous fluid; 
 (b) the more viscous fluid and the less viscous fluid contain the same gel stabilizer and further wherein the amount of gel stabilizer in the less viscous fluid is less than the amount of gel stabilizer in the more viscous fluid; 
 (c) the less viscous fluid is less stable than the more viscous fluid by the amount of pH buffer present in the less viscous fluid; or 
 (d) the more viscous fluid and the less viscous fluid contain the same viscosifying agent and wherein the amount of viscosifying agent in the less viscous fluid is less than the amount of viscosifying agent in the more viscous fluid.